In a known type of color electrophotographic (EP) printer, four stations associated with four colors, yellow, magenta, cyan, and black, are provided. Each station includes a laser printhead that is scanned to provide a latent image on the charged surface of a photoconductive (PC) drum. The latent image on each drum is developed with the appropriate color toner and transferred onto an intermediate transfer member (ITM) belt. A composite layer image is accumulated on the belt by passing each of the four color stations in turn. The composite layer image is then transferred to a substrate at a second transfer station. The second transfer station may comprise a transfer roll and a backup roll engaging the inside of the ITM belt, such as disclosed in U.S. Pat. No. 6,681,094, the disclosure of which is incorporated herein by reference.
For certain toner materials, such as a chemically process toner material, a high compressive load, e.g., 36 g/mm of roll contact length, is required to ensure proper toner image transfer from the ITM belt to a substrate.
Traditionally, the transfer roll may comprise an outer compliant layer. Such a layer can be deformed permanently, i.e., compression set, if left inactive and under a high compressive load, e.g., 36 g/mm of roll contact length, for prolonged periods of time. The deformation can lead to print defects.
It is known to provide a transfer roll retraction mechanism to release the transfer nip load when a printer is inactive. However, it is believed that such retraction mechanisms require a feedback system comprising one or more sensors in combination with a controller to control the position of the retraction mechanism and, hence, the transfer roll relative to the ITM belt and backup roll.
If would be desirable to have a transfer roll retraction mechanism not requiring a sensor feedback system so as to reduce the cost of the mechanism.